This Friday, February 15 at 09:24 PM South African Standard Time, a near-Earth asteroid named 2012 DA14 will pass the Earth at a distance of about 27 700 km from the Earth's surface (which corresponds to a distance about twice the Earth's diameter). This may sound like a large distance to us, but in space terms its a very close shave! The asteroid will pass within the Moon's orbit and it will be closer to Earth than weather and communications satellites in geosynchronous orbit. Fortunately, calculations show that the asteroid will not hit the Earth during this pass and it is extremely unlikely to hit any man made satellites. The asteroid will next return to our neighbourhood in 2020.
It was originally thought that there might be a small chance of a collision with Earth on its next approach in 2020, but this has now been ruled out and astronomers have determined that there is no risk of impact for the next hundred years.
Unfortunately, the asteroid fly-by won’t be visible to the naked eye because it is too small, however it should be visible using binoculars or small telescopes. Details of the asteroid's position can be found at www.heavens-above.com.
2012 DA14 was discovered on February 23, 2012, by astronomers at La Sangra Astronomical Observatory, Spain. It is a near-Earth asteroid, essentially a lump of rock, with an estimated diameter of about 45 metres and an estimated mass of about 130 000 tons. The 2013 passage of 2012 DA14 by Earth is a record close approach for a known object of this size and the eighth-closest approach by a known asteroid on record. 2012 DA 14 belongs to the class of asteroids known as Apollo asteroids.
Apollo asteroids are defined as having a minimum distance from the Sun less than 1.017 times that of the Earth, and a semi-major axis (the radius of their orbit measured across the long part of the ellipse) greater than the Earth's. These are asteroids with orbits that cross the orbit of the Earth and thus are potential threats to our planet.
As of February 07 this year, 9683 Near-Earth objects (asteroids and comets) have been discovered. Astronomers believe that there are approximately 500 000 near-Earth asteroids the size of 2012 DA14 and more than a million near-Earth asteroids greater than 40 metres in diameter! On average, an object similar in size to 2012 DA14 is expected to get this close to Earth about once every 40 years. However, a collision with Earth by an object of this size is expected on average only once every 1200 years.
The Earth's atmosphere protects us from most asteroids smaller than around 40 metres in diameter, (corresponding to an impact energy of about 3 megatons). From 40 metres up to about 1 kilometre diameter, an impacting near-Earth asteroid can cause regional devastation. The impact of an asteroid just slightly smaller than 2012 DA14 (30-40 metres across) in 1908 is believed to have flattened about 1200 square kilometers of forest in and around the Podkamennaya Tunguska River in Russia.
Above an energy of a million megatons (corresponding to an asteroid diameter of about 2 kilometres), an impact will produce serious environmental damage on a global scale. The most likely outcome from a collision with an asteroid of this size would be an "impact winter" with the loss of crops worldwide leading to starvation and disease. On average, asteroids of this size are expected to collide with the Earth once or twice every million years. Even larger impacts can cause mass extinctions, like the one that is thought to have killed the dinosaurs 65 million years ago (15 kilometres diameter and about 100 million megatons) but these are incredibly rare.
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Dr Nicola Loaring
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